Hollow fiber blood oxygenator

ABSTRACT

An exchanger includes an outer casing having an inlet port and an outlet-port for a first fluid, and an inlet port and an outlet port for a second fluid, and a bundle of hollow fibers located within the outer casing and being in flow communication with the inlet and outlet port for the second fluid. A central core is located in the outer casing and the bundle of fibers is arranged around the central core. The central core includes an inlet manifold connected to the first fluid inlet port, and an outlet manifold connected to the first fluid outlet port.

This application is a continuation, of application Ser. No. 08/050,641,filed Apr. 22, 1993, now abandoned, which is a continuation-in-part ofapplication Ser. No. 07/970,781 filed Nov. 3, 1992 now allowed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to hollow fiber membrane exchangers. While theinvention is subject to a wide range of applications, it is especiallysuited for use in oxygenating blood and will be particularly describedin that connection.

2. Description of the Related Art

During open heart surgery, natural cardiovascular activity is suspended,which causes the lungs to collapse. It is therefore necessary tosimulate the function of the lungs, which replaces carbon dioxide in theblood with oxygen. Blood oxygenators serve this function. A typicalhollow fiber blood oxygenator includes a bundle of hollow fibersextending through a blood chamber for conveying oxygen into the bloodchamber and for removing carbon dioxide from the blood therein.Specifically, the fibers are constructed of a membrane material thatacts as a boundary between extracorporeal blood flow and oxygen flow. Asblood flows on the outside of the fibers and oxygen passes through thehollow fibers, a gas exchange occurs wherein oxygen passes through thefiber walls and into the blood and carbon dioxide passes, in theopposite direction, from the blood into the interior of the hollowfibers.

There are multiple and sometimes conflicting parameters that must beconsidered when designing a hollow fiber membrane exchanger. Forexample, the longer blood remains in contact with the fibers, thegreater the amount of gas exchange that may occur. Thus, it may bedesirable to design the oxygenator so that the length of the flow pathof the blood relative to the hollow fibers is maximized to therebymaximize contact between blood and the hollow fibers. On the other hand,it is desirable to construct an exchanger that is as small and compactas possible. Thus, the desire to build a compact unit is somewhatconstrained by blood flow path length requirements.

Biocompatibility is also a factor that must be considered in exchangerdesign. For example, membrane exchangers are typically manufactured frommultiple components that are joined together with adhesives. However, inorder to minimize the possibility of bioincompatibility between theblood and the materials that make up the exchanger, it is preferable tominimize the number of materials with which extracorporeal circulatingblood comes into contact. Thus, while adhesives may be necessary, it isbeneficial to limit the amount of adhesive that is located in the bloodflow path.

Finally, gas exchange requirements, which are often dependent upon aparticular use, also place constraints on the ultimate design of anexchanger. For example, adults typically have greater gas exchangerequirements than children, and therefore require a larger membranecompartment. Therefore it is common for manufacturers to offerexchangers of varying sizes/each size being designed for a particulargas exchange requirement, and each size employing its own uniquely sizedparts. However, this is not cost effective. From a cost efficiencyperspective, it is easier to develop economies of scale if many of thesame parts can be used regardless of the membrane size. Thus, it ispreferable to provide a membrane exchanger that is constructed of asmany standard parts as possible for use with membranes of varying sizes.

SUMMARY OF THE INVENTION

An advantage of the invention is to provide an exchanger that maximizesthe time during which extracorporeally circulating blood contacts thehollow fibers while at the same time minimizing the size of theexchanger.

Another advantage of the invention is to provide an exchanger whichminimizes possibility of bioincompatibility.

A further advantage of the invention is to provide an exchanger that canbe manufactured economically in different sizes.

Additional features and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

To achieve the objects and in accordance with the purposes of theinvention, as embodied and broadly described herein, the inventioncomprises an exchanger including an outer casing having an inlet portand an outlet port for a first fluid, and an inlet port and an outletport for a second fluid. A bundle of hollow fibers is located within theouter casing, and is in flow communication with the inlet port and theoutlet port for the second fluid. A central core is located in the outercasing and the bundle of fibers is arranged around the central core. Thecentral core includes an inlet manifold connected to the first fluidinlet port, and an outlet manifold connected to the first fluid outletport.

Preferably the central core has a substantially elongated tubular shapeand the inlet and outlet manifolds are recessed in the core and extendalong substantially the entire length of the core.

It is also preferable for the outer casing and central core to be sizedand shaped so that the bundle of fibers sandwiched therebetween variesin density, the bundle having a lower density in areas adjacent theinlet and outlet manifolds than in areas spaced from the inlet andoutlet manifolds.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention, and together with the description, serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the typical interconnection of apatient to a membrane exchanger such as the exchanger of the presentinvention;

FIG. 2 is an oblique drawing of a membrane exchanger module andinterconnected heat exchanger module in accordance with the presentinvention;

FIG. 3 is a cross-sectional front view of the apparatus illustrated inFIG. 2;

FIG. 4 is an oblique view of the core illustrated in FIG. 3;

FIG. 5 is a cross-sectional view of the core illustrated in FIG. 4;

FIG. 6 is an enlarged detail of a portion of FIG. 3;

FIG. 7 is a cross-sectional side view taken along the line VII--VII inFIG. 3 where the cross-sectional blood flow pattern is illustrated;

FIG. 8 illustrates the cross-sectional blood flow pattern as occurs inthe cross-sectional view of FIG. 3; and

FIG. 9 illustrates fiber orientation of the bundle of hollow fibersillustrated in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, an example of which is illustrated in theaccompanying drawings. Wherever possible, like reference numerals areused to designate the same or like parts.

When the membrane exchanger of the present invention is used tooxygenate blood and remove carbon dioxide therefrom, the exchanger maybe connected to a patient under treatment in a manner illustrated inFIG. 1.

As illustrated in FIG. 1, blood tubing is connected between the venoussystem of a patient and venous reservoir 10. A blood pump 12 conveysblood from reservoir 10 to heat exchanger 14. In the heat exchanger, thetemperature of the blood is altered to reach a desired treatmenttemperature and the blood is then conveyed to a membrane lung 16, which,in the case of the present invention is a hollow fiber oxygenator. Frommembrane lung 16, the treated blood is returned to the arterial systemof the patient. In this manner the patient's gas exchange needs and bodytemperature can be regulated during complex procedures such ascardiovascular bypass surgery.

The present invention provides an apparatus for accomplishing thesevital gas exchange and temperature regulation needs. As illustrated inFIG. 2, a preferred embodiment of the invention includes oxygenationmodule 18 and heat exchanger module 20.

In accordance with the present invention there is provided a gasexchanger having an outer casing with an inlet port and an outlet portfor a first fluid, and an inlet port and outlet port for a second fluid.As illustrated in FIGS. 2 and 3, the outer casing includes asubstantially cylindrical outer tube 22 which is preferably constructedof a transparent plastic material. The outer casing also includes aninlet cap 24 and an outlet cap 26, disposed on opposite ends of tube 22.Inlet cap 24 includes a first fluid inlet port 28 located therein forpermitting a first fluid to enter the interior of oxygenation module 18.The first fluid may exit oxygenation module 18 through outlet port 30located in outlet cap 26. Additionally, a second fluid inlet port 29 isprovided in inlet cap 24, and a second fluid outlet port 31 is providedin outlet cap 26. When the invention is used in connection with bloodoxygenation, the first fluid is blood which enters and exits exchangermodule 18 through ports 28 and 30, respectively, and the second fluid isoxygen which enters and exits module 18 through ports 29 and 31,respectively. Ports 28 and 30 include inwardly tapered male endsextending toward the inside of cap 24 and 26.

In accordance with the present invention there is also provided a bundleof hollow fibers located within the outer casing and being in flowcommunication with the inlet port and the outlet port for the secondfluid. As embodied herein and as illustrated in FIG. 3, a bundle ofhollow fibers 32 is arranged in a tubular formation within outer tube22. As illustrated in FIG. 9 the fiber bundle consists of a doublelayer, cross-wound hollow fiber mat of which is rolled upon itself toform the bundle illustrated in cross-section in FIG. 3. Each of thelayers of fibers 34, 36 includes a plurality of fibers arranged inparallel and stitched together with parallel stitching 37 to limit thefibers movement relative to each other. The fibers of adjacent layers ofmats 34, 36 are angled with respect to each other to prevent adjacentlayers 34, 36 from nesting within one another. For example, the fibersof one mat may define an angle of 22° with respect to the fibers of theother mat. The ratio of the distance between two adjacent lines ofstitching 37 to the distance between two adjacent fibers may be about45.

Many different types of hollow fiber may be employed, depending upondesired use. In a preferred embodiment for use in a blood oxygenator,the fibers may be constructed of polypropylene microporous material,each fiber having an outer diameter of about 380 μm and an innerdiameter of 280 μm. An acceptable average density may be approximately14.3 fibers per centimeter. After the mats 34, 36 are rolled to formbundle 32 and each fiber is closed at both ends by pinching, the ends38, 40 of bundle 32 are potted within tube 22 using a resin to therebyseal the fibers together at their ends and to seal bundle 32 within tube22. After the resin dries, the ends 38, 40 are shaved to reopen thefibers so that fluid, such as oxygen may flow therethrough.

In accordance with the invention there is also provided a central corelocated within the outer case, and around which the bundle of fibers isarranged, the central core including an inlet manifold connected to thefirst fluid inlet port and an outlet manifold connected to the firstfluid outlet port.

As embodied herein, and as best illustrated in FIGS. 4, 5, and 6,central core 42 includes inlet manifold 44 and outlet manifold 46.Central core 42 has a generally cylindrical tubular shape, withmanifolds 44 and 46 being recessed in central core 42 in a diametricallyopposed orientation and each manifold extending towards the central axisof core 42. The location of manifolds 44 and 46 within the centerportion of the core conserves space and enhances blood flow throughhollow fiber bundle 32, as is described later in greater detail.

Inlet manifold 44 and outlet manifold 46 each include a generallyV-shaped concavity extending substantially along the length of core 42.A pair ports 48 and 50 are located within core 42 and are respectivelyconnected to inlet manifold 44 and outlet manifold 46. Ports 48 and 50each include an outwardly tapered apertures for respectively receivinginwardly tapered male ends of first fluid inlet port 28 and first fluidoutlet port 30, previously described. Ports 28 and 48 mate in apress-fitting relationship so that no adhesive is required to join theports. Similarly, ports 30 and 50 engage each other in a press-fitmanner.

Manifolds 44 and 46 each include central ribs 52 and 54 that run thelength of their respective manifold and which each include distal edgeswhich are recessed from the outer diameter of central core 42, as isindicated by the dashed lines in FIG. 6. In other words the outside ofthe core surface defines an arc, and the distal edges of the ribs arelocated below this arc. Ribs 52 and 54 include apertures 56 and 58 (asbest illustrated in FIG. 5) respectively located in the regions of inletport 48 and outlet port 50. Apertures 50 and 56 enhance even blood flowon opposite sides of ribs 52 and 54.

The double fiber mat previously described is wrapped around core 42 inorder to form hollow fiber bundle 32 and is sandwiched between core 42and tube 22. The previously described potting on ends 38 and 40 ofbundle 32 seal the ends between core 42 and tube 22. Caps 24 and 26 arerespectively spaced from potted ends 38 and 40 to define circular gasinlet and outlet manifolds 55 and 57, respectively.

As illustrated in FIG. 7, the concave nature of manifolds 44 and 46 incombination with the previously described recessed nature of ribs 52 and54 provide reduced support for hollow fiber bundle 32 in the regions ofthe manifolds 44 and 46. Thus, the fiber density in the regionsimmediately surrounding and above the concavities of the manifolds 44and 46 is less than the fiber density in all other areas of the bundle.This reduced manifold region bundle density enhances even absorption ofblood into the fiber bundle as blood exits the inlet manifold, enhanceseven return of blood to the outlet manifold, and generally provides amore even distribution of blood through the bundle of hollow fibers.

The invention may also include connecting means for sealing at least oneof caps 24 and 26 to outer tube 22. As embodied herein the connectingmeans may be any type of conventional or non-conventional structureincluding grooves, adhesives or mechanical connections. Preferably, theconnecting means includes angled circumferentially disposed flanges 64and 66 extending from tube 22, and corresponding ridges 60 and 62 incaps 24 and 26. An advantage of this preferred embodiment of theinvention is that varying capacity exchangers may be manufactured frommany of the same components, thereby obviating the need to manufactureand many different parts for different capacity exchangers.Specifically, if a manufacturer wishes to construct exchangers withvarying thickness hollow fiber bundles, other than the amount ofmembrane itself, the only structure that need be varied is the outertube 22. This feature results from the central orientation of the inletand outlet manifolds, as well as the unique seal of the preferredconnecting means between outer tube 22 and caps 24 and 26. Specifically,caps 24 and 26 are oversized relative to outer tube 22 so that annularspaces 25 and 27 are formed between the outer wall of tube 22 and theinner wall of caps 24 and 26. Each of caps 24 and 26 include annulargrooves 60 and 62, respectively. Corresponding angled flanges 64 and 66extend from outer tube 22 and mate with annular grooves 60 and 62. Resinis deposited about grooves 60 and 62 to seal the circumferential angledflanges 64 and 66 within grooves 60 and 62, respectively. Thus, aleakproof seal is attained between caps 24, 26 and tube 22.

With this arrangement, a manufacturer can construct exchangers ofvarying capacity using a standard sized inner core 42 and caps 24 and26. In order to accommodate a thicker hollow fiber membrane bundle, anouter tube 22 of greater diameter is used, which includes angled flanges64 and 66 which are decreased by the same amount of the tube diameterincrease so that the angled flanges mesh with grooves 60 and 62 of caps24 and 26, respectively. Likewise, if an exchanger with a smallercapacity hollow fiber bundle is desired, the diameter of outer tubing 22is decreased, and the radial length "L" (as shown in FIG. 3) of flanges64 and 66 are increased by the same amount. Thus, the preferredembodiment of the invention maximizes the number of interchangeableparts between varying capacity exchangers, thereby making it easier fora manufacturer to achieve economies of scale.

The exchanger configuration of the invention with its centrally orientedcore permits a blood oxygenator to be molded as a single unit which isan advantage from both a manufacturing and a safety point of view.Specifically, since the core is formed of a single molded part, itincludes no bonds which would be necessary if the core was made frommore than one part. Elimination of such bonds is beneficial since theyare susceptible to leakage under pressure.

The present invention may also include a heat exchanger module 20integrally connected with exchanger module 18. The purpose of heatexchanger module 20 is to control the temperature of the fluid beingtreated. Specifically, when the invention is used in connection withoxygenation of blood during cardiovascular bypass surgery, heatexchanger module 20 is used to regulate the temperature of the patient'sblood. This is accomplished by providing a heat exchanger casing 68which is divided into two separate compartments by a folded heatconducting sheet 70. Heat conducting sheet 70 may be constructed ofstainless steel, metal foil, or any other suitable heat conductingmaterial. Heat exchange inlet port 72 and heat exchange outlet port 74permit a heat exchange fluid to flow along a first side of the foldedfoil membrane 70 as indicated by arrows 76. Blood inlet port 78 permitsblood to flow on an opposite side of foil membrane 70 as indicated byarrows 80. As heat exchange fluid and blood pass along opposite sides ofsheet 70, a heat exchange takes place across sheet 70, and thetemperature of the blood is altered. Blood outlet 82 of heat exchangermodule 20 is directly connected to blood inlet port 28 of exchangermodule 18. A stainless steel thermometer well 84 extends into the bloodflow path adjacent heat exchanger outlet port 82 so that bloodtemperature may be monitored during the medical procedure.

The invention may employ any type of conventional heat-exchanger and, inits broadest sense, the invention need not include heat exchanger module20 integrally connected with exchanger module 18. However, the fixedinterconnection is preferred because it reduces the number of tubinghook-ups required during the medical procedure, thereby minimizing thepossibilities of leakage and contamination. In addition, the directinterconnection shortens the overall length of the extracorporeal bloodcircuit.

Another feature of the invention which permits a shortening of theextracorporeal blood circuit includes pivotal venous reservoir mount 86located atop gas exchanger module 18. Mount 86 includes a table 88having a rotatable mounting tube 90 extending therefrom. Mounting tube90 rotates within a collared bracket 92 which is fixed to gas exchangemodule 18. This structure permits the venous reservoir to be maintainedin the closest possible proximity to the exchanger, thereby limiting therequired length of blood tubing between the venous reservoir and theexchanger.

Operation of the invention will now be described with references toFIGS. 3, 7, and 8. Initially, a venous reservoir (not shown) is placedon rotatable mount 86, and is connected through a pump to inlet port 78of heat exchanger module 20. Ports 72 and 74 of heat exchanger module 20are connected to a heat exchange fluid circuit (not shown). The venousreservoir is also connected to the vascular system of a patient, andblood outlet port 30 is connected to the vascular system of a patient.

After the apparatus is primed in a conventional manner, treatment iscommenced by flowing blood from the venous reservoir into blood inletport 78 of heat exchanger module 20. As the blood passes along one sideof folded sheet 70 within heat exchanger module 20, heat exchange fluidssimultaneously passes along an opposite side of folded sheet 70 to alterthe temperature of the blood. This temperature is monitored by atemperature probe (not shown) which is disposed in well 84. Blood thenexits heat exchanger module 20 through outlet port 82 and enters gasexchange module 18 through inlet port 28 in cap 24. Blood then flowsinto inlet manifold 44, and enters hollow fiber bundle 32 at an angletransverse to the radius of bundle 32, as indicated by arrows 80. Asindicated by the arrows in FIGS. 7 and 8, the blood flow path of theblood through bundle 32 is maximized in as much as the blood flows notonly from the inner diameter to the outer diameter of core 32, but alsoflows halfway around the circumference of core 32 where it is collectedin outlet manifold 46.

Simultaneously, oxygen enters the apparatus through gas inlet port 29where it enters the potted inlet end 38 of hollow fiber bundle 32.Oxygen then passes through the hollow fibers of the bundle and isreleased into the blood as blood flows around the fibers of bundle 32.As oxygen enters the blood, carbon dioxide exits the blood and entersthe interior of the hollow fibers. The carbon dioxide then passesthrough the potted outlet end 40 of hollow fiber bundle 32 and exits theapparatus through gas outlet port 31. In this manner, temperatureregulation and gas exchange of a fluid such as blood may be achieved.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. An exchanger, comprising:an outer casing havingan inlet port and an outlet port for a first fluid, and an inlet portand an outlet port for a second fluid; a bundle of hollow fibers locatedwithin the outer casing, and being in flow communication with the inletand outlet port for the second fluid; and a central core located in theouter casing and around which the bundle of fibers is arranged, thecentral core including an inlet manifold connected to the first fluidinlet port, and an outlet manifold connected to the first fluid outletport.
 2. An apparatus as claimed in claim 1, wherein the central corehas a substantially elongated tubular shape of predetermined length, andthe inlet and outlet manifolds extend along substantially the entirelength of the central core.
 3. An apparatus as claimed in claim 2,wherein the inlet and outlet manifolds are located in the tubularcentral core in a substantially diametrically opposed orientation.
 4. Anapparatus as claimed in claim 2, wherein the blood inlet and outletmanifolds have a concave shape extending towards a center of the centralcore.
 5. An apparatus as claimed in claim 1, wherein the inlet andoutlet manifolds are recessed in the central core.
 6. An apparatus asclaimed in claim 1, wherein at least one of the inlet and outletmanifolds includes a central rib having a distal edge.
 7. An apparatusas claimed in claim 6, wherein a distal edge of a rib is located belowan arc defined by the outside core surface.
 8. An apparatus as claimedin claim 1, wherein the outer casing and the central core are sized andshaped to maintain the bundle of fibers at a first packing density in aregion of the blood inlet manifold and at a second packing density,greater than the first packing density, in a region radially spaced fromthe blood inlet manifold.
 9. An apparatus as claimed in claim 1, whereinthe outer casing and the central core are sized and shaped to maintainthe bundle of fibers at a first packing density in a region of the bloodoutlet manifold and at a second packing density, greater than the firstpacking density, in a region radially spaced from the blood outletmanifold.
 10. An apparatus as claimed in claim 1, wherein the outercasing and the central core are sized and shaped so that the bundle offibers sandwiched therebetween varies in packing density, the bundlehaving a lower packing density in areas adjacent the inlet and outletmanifolds than in areas spaced from the inlet and outlet manifolds. 11.An apparatus as claimed in claim 1, wherein the outer casing includes anouter tube having a cap disposed on an end thereof, the exchangerfurther including connecting means for sealing the cap to the outertube.
 12. An apparatus as claimed in claim 11, wherein the connectingmeans includes an angled flange extending from the outer tube, and thecap includes a groove for receiving a portion of the angled flange. 13.An apparatus as claimed in claim 11, wherein the cap includes a wallextending substantially parallel to the outer tube, the wall of the capbeing spaced from the tube.
 14. An apparatus as claimed in claim 11,wherein the cap engages the central core in a press-fit manner.
 15. Anapparatus as claimed in claim 14, wherein at least one manifold includesan inwardly flared tubular end and the cap includes an outwardly flaredtubular fitting that engages the flared tubular end in a press fitmanner.
 16. An apparatus as claimed in claim 1, further including a heatexchanger integrally connected thereto.
 17. An apparatus as claimed inclaim 1, further including a quantity of potting material located atopposite ends of the bundle of hollow fibers for sealing the fibers toeach other and for sealing the bundle within the outer casing betweenthe outer casing and the core.
 18. An apparatus as claimed in claim 1,wherein the first fluid is blood and the second fluid is oxygen.
 19. Ablood oxygenator, comprising:an outer casing having an inlet port and anoutlet port for blood, and an inlet port and an outlet port for oxygen;a bundle of hollow fibers located within the outer casing, and being inflow communication with the oxygen inlet and outlet ports; and a centralcore located in the outer casing and around which the bundle of fibersis arranged, the central core including an inlet manifold connected tothe blood inlet port, and an outlet manifold old connected to the bloodoutlet port.
 20. An exchanger, comprising:an outer casing having aninlet port and an outlet port for a first fluid, and an inlet port andan outlet port for a second fluid; a bundle of hollow fibers locatedwithin the outer casing, and being in flow communication with the inletand outlet port for the second fluid; and a central core having asubstantially elongated tubular shape of predetermined length located inthe outer casing and around which the bundle of fibers is arranged; aninlet manifold recessed in and extending along substantially the entirelength of the central core, the inlet manifold being connected to thefirst fluid inlet port; and an outlet manifold recessed in and extendingalong substantially the entire length of the central core, the outletmanifold being connected to the first fluid outlet port.